Measure exposure time - photo resistor

On: Fri, Apr 26, 02 12:42:05 PM

Thilo K. wrote:

Hello. Iīve heard one can measure the relative energy of a
lightbeam per mmē or mē by using a photo resistor.
I bought one 2 years ago. What I can do very well is
measuring the ratio - you know which one :) - but not the
energy to figure out the exposure time.
Do you know how to get the needed time ?
Besides, the value of the resistor is indirect proportional
to brightness. Since there is no value given that
represents "darkness", there has only been successful
measurement of the ratio so far.
Any suggestions ?

RESPONSES

Jean Dufrasne - Sun, Apr 28, 02 02:03:20 PM

Hi Thilo,
Found on the Steve Michael's site.
http://www.3dimagery.com/exposure.html
Steve uses a solar cell but maybe you can use your
photoresistor just by changing scale on your VOM (select
Resistor instead of Volt) and apply the same formula ?
Can somebody confirm this ?
See you.
Jean.62.235.20.20

Thilo K. - Tue, Apr 30, 02 01:52:50 PM

Hi Jean,
thank you very much for the URL.
Occasionally, I saw it a week ago. We have also had some
email exchange. But - ultimately - he seeks for the right
time by "trial and error". Something that isnīt bad at all
as a matter of course.
But what I want is to determine how long it takes by using
a formula, which is physically correct without experimental
factors; that means there should be no correction, no
enhancement - at least no great one - neccessary, if a
setup is changed.
Can you help ?
Something different: You might be using PFG-01. So maybe as
you know, color changes from green to red in reflection
holograms if the exposure time is increased.
Do I expose the film long enough, if the picture is almost
red ?145.254.230.110

Dooley - Tue, Apr 30, 02 03:17:47 PM

It is my understanding that if the pfg01 hologram is
developed using jd2 that the longer you expose it will turn
green and eventualy blue. Also it is hard to controll all
of the factors as the humidity as well as temperature affect
the exposure time. Lately with the d&s laser system running
at aprox. 27mW and the pfg01 with jd2 dev. I have been
exposing for 10 seconds. With the pfg03 and jd4 dev. 10
sec. is also a good time for my particular set up. I came
to this conclusion by many trials and a detailed logbook for
each exposure.198.206.243.1

Thilo K. - Wed, May 01, 02 06:14:56 AM

Hello Dooley,
what kind of entries did you add to your 'detailed logbook'
and how did you get them ?145.254.230.254

Thilo K. - Wed, May 01, 02 06:29:18 AM

Additionally, some information that might be useful:
developer: Neutol
P(Laser): as itīs used it is within the bounds of 5mW and
8mW
film: PFG-01
one-beam-reflection exposure time: 30s145.254.230.254